metadata: Exclude field::type_name from metadata validation

[lexnv]

The #591 presented a metadata validation issue detected on the Snowbridge parachain.

The metadata validation would reject extrinsics due to the following difference in metadata:

Source	Metadata
snowbridge	"typeName": "/«/ u32 /»/"
polkadot	"typeName": "u32"

This PR removes the hashing of the typeName as the unique deterministic representation of the field is deduced from its type and name.

Testing

Utilizing the metadata provided in the issue:

subxt-cli -- codegen --file ours.metadata.scale > ours.rs
subxt-cli -- codegen --file theirs.metadata.scale > theirs.rs

diff ours.rs theirs.rs
#ok - identical hashes for validation

[jsdw]

LGTM, thanks!

[TarikGul]

Interesting, I never really thought about it but omitting the check for type_name makes sense since you can do validation through type, and name itself as @lexnv mentioned.

Nice job 👍